The Legion of the Bouncy Castle Java Cryptography API provides a lightweight cryptography API in Java, a provider for the JCE and JCA, a clean-room implementation of the JCE 1.2.1, generators for Version 1 and Version 3 X.509 certificates, generators for Version 2 X.509 attribute certificates, PKCS12 support, and APIs for dealing with S/MIME, CMS, OCSP, TSP, CMP, CRMF, EAC, DVCS, OpenPGP, DTLS, and TLS. Versions are provided for the J2ME, and JDK 1.0-1.7.

Libmcrypt is a library which provides a uniform interface to several symmetric encryption algorithms. It is intended to have a simple interface to access encryption algorithms in ofb, cbc, cfb, and ecb modes. The algorithms it supports are DES, 3DES, RIJNDAEL, Twofish, IDEA, GOST, CAST-256, ARCFOUR, SERPENT, SAFER+, and more. The algorithms and modes are also modular so you can add and remove them on the fly without recompiling the library.

Linux VPN Masquerade allows you to use an IPSec or PPTP VPN host (client or server) behind a Linux masquerading firewall. No more hogging the cable modem when you need to connect to the office network.

Mailcrypt is an Emacs Lisp package which provides a simple interface to public key cryptography with PGP/GPG. Mailcrypt makes strong cryptography a fully integrated part of your normal mail and news handling environment.

mcrypt is a program for encrypting files or
streams. It is intended to be a replacement for
the old UNIX crypt. It uses well-known and
well-tested algorithms like BLOWFISH, AES,
ARCFOUR, CAST-128, and more in several modes of
operation. It also has a compatibility mode with
the old UNIX crypt program and the des program
found in Solaris.

The MD5 message digest library implements the MD5 message digest algorithm specified in RFC 1321 directly from the specification, without copying from the reference implementation and therefore without requiring mention of RSA when used. It uses the same unrestricted-distribution license as zlib.

The modular syslog allows for an easy implementation of input and output modules. The modules that mantain compatibility with its precursor are included in the standard distribution along with four modules: om_peo (an implementation of PEO-1 and L-PEO, two algorithmic protocols for integrity checking), om_mysql and om_pgsql (modules that sends output to a mysql and postgresql database, respectively) and om_regex (a module that allows output redirection using regular expressions).

mxCrypto is an extension package that provides OO-style access to the cipher algorithms and hash functions included in OpenSSL/SSLeay, a very nifty cryptographic library originally written by Eric Young and now maintained by the OpenSSL team. Its main purpose is filling in the missing parts in Andrew Kuchling's pycrypt export package with high quality implementations. Due to the ITAR export restrictions on cryptographic software, Andrew's implementations are not legally downloadable from outside the US.